James A. Sommers

Thermodynamics of the lanthanide halides I. Heat capacities and Schottky anomalies of LaCl3, PrCl3, and NdCl3 from 5 to 350 K

Abstract The heat capacities of LaCl 3 , PrCl 3 , and NdCl 3 have been measured from 5 to 350 K by adiabatic calorimetry. No co-operative thermal anomalies were seen in the temperature range investigated but substantial magnetic heat-capacity contributions of the non-cooperative (Schottky) type were found. Subtraction of the heat capacity of the diamagnetic and isostructural LaCl 3 from those of the paramagnetic members yields experimental Schottky heat-capacity contributions which are compared with heat capacities derived from spectroscopically determined energy levels. Small discrepancies between the calculated and experimental contributions are probably due to differences in lattice heat capacities between LaCl 3 and the others. The values of {( S o (298.15 K) − S o (0)}/cal th K −1 mol −1 are for LaCl 3 and NdCl 3 , 32.88 and 36.67. Due to the possibility of a low-temperature phase transition, the entropy of PrCl 3 covers only the experimental range of this research and that of Colwell, Mangum, and Utton. { S o (298.15 K) − S o (0.294 K)} for PrCl 3 is 36.64 cal th K −1 mol −1 .

Heat capacity of hafnium mononitride from temperatures of 5 to 350 K: An estimation procedure

Measurements of the heat capacity by quasi-adiabatic, intermittent energy increments from 5 to 350 K show small high heat-capacity anomalies near 7 and 10 K which are attributed to superconducting transitions seen by magnetic measurements on the same carefully synthesized and well-characterized sample of (Hf0.934Zr0.057)(N0.97). Although no previous heat capacity measurements over the cryogenic region are known, the estimated 298.15 K standard entropy values (S/R) vary in the literature from about 200 per cent higher to 5 per cent lower than our measured value of (5.28±0.01)R−1 when the formula is represented as above. A simple scheme to represent and predict values based on both molar volumes and atomic masses for related materials is presented which seems more reliable on a limited sample than do others despite the intrusion of lanthanide contraction.

Aftereffects following β-decay of181Hf1

Time differential perturbed angular correlation spectra of181Ta produced by beta decay of181Hf in monoclinic ZrO2 have been measured over a temperature range 10K to 1300K. If times near t=0 are excluded, G2(t) is well fitted by a standard single site model for nuclei subject to an interaction with a static electric field gradient. For high purity samples, the effective anisotropy A2 is equal to its expected value above 200°C but decreases abruptly by approximately a factor of two for lower temperatures. This unusual decrease, which does not occur in natural crystals or in Nb-doped powders, is attributed to an aftereffect of the beta emission that populates with approximately 50% probability an electron trap located about one eV below the conduction band. At low temperatures, this trapped electron causes the Ta nucleus to relax rapidly and contributes to G2(t) only near t=0. At high temperatures or in doped samples the electron escapes quickly enough to have negligible effect on G2(t).

Dynamics and thermodynamics of tetragonal zirconia determined by 111In/Cd TDPAC

For several years this research group has been using 111In/Cd TDPAC to study oxygen vacancies in pure and lightly doped zirconia powders at temperatures up to 1400°C. This paper includes a brief survey of important results from those studies and some recent results. In particular, our new measurement showing negligible relaxation due to vacancy hopping above 600°C provides a major breakthrough in our ability to analyze PAC data and to determine accurately hopping and trapping rates and enthalpies for vacancies in tetragonal zirconia.

Structural and electronic properties of indium-doped YBa2Cu3Oσ

We have measured x-ray diffraction patterns and Meissner flux exclusion of YBa 2 Cu 3 O σ containing indium. All samples were synthesized at temperatures near 940 °C, and the data indicate the indium atomic solubility to be approximately 3% per formula unit. At the solubility limit T c is reduced from 92.7 K to 91.3 K relative to undoped samples, and the total magnetic flux excluded is reduced from approximately 40% to about 10%. For samples of formula In x Y 1− x Ba 2 Cu 3 O σ concentrations of other Y–Ba–Cu oxide phases are low and do not depend systematically on x . These results indicate that indium substitutes predominantly for yttrium when x is small.